1. Field of the Invention
The invention relates to a telescopic vibration damper including a pressure tube filled with a damping medium, a piston rod arranged to move axially in the pressure tube, an intermediate tube in which the pressure tube is arranged to move axially, an annular chamber between the pressure tube and the intermediate tube, a flow connection between the pressure tube and the annular chamber, and a compensating chamber which accommodates the displaced volume of the components that can be telescoped toward one another.
2. Description of the Related Art
In conventional vibration dampers, the stroke length of the piston rod is determined by the length of the pressure tube minus a dead length for a bottom valve or a compensating chamber. In particular in the case of automobiles, the trunk should not be restricted by a dome for the vibration damper. Vibration dampers installed horizontally are often found in combination with unfavorable axle constructions.
DE-U 1 995 279 discloses a telescopic vibration damper which has a pressure tube in which a piston rod can be displaced axially. The pressure tube can be displaced axially in relation to an intermediate cylinder which, with a container tube, forms a compensating chamber. Present on the pressure tube, in the pulling and compressing directions, are stop means which, beginning at the maximum retraction or extension position of the piston in the pressure tube, carry along the intermediate cylinder with a form fit during the further retraction or extension movement, and therefore a stroke length is achieved which is considerably greater than that of a conventional vibration damper.
One drawback of this specific vibration damper can be seen in the fact that, in a central stroke range, there is no positive assignment between the piston rod, the pressure tube and the intermediate cylinder. Depending on the frictional relationships, an indeterminate stroke position combination of the aforementioned subassemblies is established. It could be the case, for example, that the piston rod has already reached the end position in the pressure tube, and the pressure tube is still retracted to the maximum in the intermediate cylinder. On the other hand, the piston rod can still be retracted to the maximum in the pressure tube, but the pressure tube can already have reached its maximum extended position in relation to the intermediate cylinder.
By means of the damping valve in the vibration damper, the extending or retracting damping medium volume is always displaced. If it is not determined which of the telescopic elements retracts, then nor is it determined what damping force is effective in relation to a specific stroke position.
It is an object of the present invention to implement a telescopic vibration damper which in every stroke position ensures an unambiguous stroke position association between the individual telescopic elements.
According to the invention, the object is achieved by the annular chamber formed by the intermediate tube and the pressure tube, and the pressure tube being separated hydraulically from the compensating chamber.
The substantial advantage of the invention is that there is a hydraulically controlled positive relationship between the movements of the piston rod and of the pressure tube, so that the volumes of the damping medium flowing through the damping valves are also predefined.
In this case, provision is made for the pressure tube to have a base at one end, in which a bottom valve that acts in the retraction direction of the piston rod is arranged. In the retraction direction, a damping valve and the bottom valve can be effective on one piston.
In a further advantageous refinement, a damping valve is arranged in the flow path from the annular chamber to the pressure tube and, during an extending movement of the pressure tube, generates a damping force. An extending movement of the pressure tube is connected to an extending movement of the piston rod, as a result of the principle, it being possible for the piston rod to have a piston with a damping valve. During an extending movement of the piston, a working chamber on the piston-rod side is compressed, the pressure being supported on a piston-rod guide connected to the pressure tube. However, the compressive force is also transmitted to the damping medium in the annular chamber between the intermediate tube and the pressure tube, the damping medium subsequently flowing into the working chamber remote from the piston rod. The damping valve achieves an additional damping force which is superimposed additively on that from the damping valve in the piston. The result, in relation to the extension speed of the piston rod, is a lower pressure difference across the respective damping valves, and therefore lower loading on the damping valves.
In order to have the damping valves become effective in a specific way, in each case a nonreturn valve is connected in parallel with the damping valve and the bottom valve.
According to an advantageous embodiment, the base accommodates the bottom valve and the damping valve.
It has proven to be advantageous if the bottom valve and the nonreturn valve acting from the pressure tube toward the annular chamber are arranged in the base, and the damping valve from the annular chamber to the pressure tube is arranged in a piston section outside the pressure tube.
Furthermore, the nonreturn valve connected in parallel with the damping valve can cooperate with the piston section. Therefore, the total space needed by the piston section is utilized optimally by the valves.
For example, in one design variant, a clamping bolt for at least one valve disk belonging to the bottom valve is fixed in the base, the clamping bolt fixing a clamping means of at least one valve disk for the damping valve that acts from the annular chamber toward the pressure tube. The bottom valve and the damping valve may be biased separately.
With regard to a progressive damping force characteristic, a pull stop spring element is arranged in the pressure tube.
Alternatively or additionally, the outward springing movement of the pressure tube is limited by a pull stop.
In addition, provision can be made for a separating piston from the pressure tube to the compensating chamber to form a part of the base in the pressure tube. With this measure, a very stable separating piston is achieved, which is of interest in particular with regard to production safety, since in the case of a separate component, care must always be taken that it is not forgotten during assembly.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.